1. Technical Field
This disclosure relates generally to communications and more particularly to driver circuitry for use in a communication device.
2. Description of Related Art
Communication systems are well known and include wireless networks, wired networks, satellite networks, and various other types of networks. Wired networks use wiring or fiber to direct communications between communication devices while wireless networks support communications wirelessly. As communications technology has advanced, integrated circuits have been developed that service both wired and wireless communications. While these “combination” integrated circuits reduce the integrated circuit count of communication devices and the cost of such devices, such integration causes problems.
Line drivers are amplification devices that service wired links for various types of digital interfaces such as Serializer/Deserializer (SERDES) and optical links, for example. These line drivers drive serialized bit stream traffic from transmitters to receivers. In many transmitter/receiver links, the bit stream traffic is constructed differentially, i.e., positive and negative legs, to reduce common mode back plane noise. Common mode back plane noise is particularly troublesome in ICs that service both wired and wireless communications because the common mode noise can result in Electromagnetic Interference (EMI) that interferes with serviced wireless communications.
With differential bit stream signals, as the positive leg transitions from logic low to logic high, the negative leg transitions from logic high to logic low. Likewise, as the negative leg transitions from logic low to logic high, the positive leg transitions from logic high to logic low. Most differential line drivers include pull up and pull down transistors in both positive and negative legs. Because the pull up and pull down transistors in each of the positive and negative legs are biased differently, the rise times of each leg differ from the fall times of each leg. This difference between rise and fall times of the differential signals causes common mode back plane noise, resulting in undesirable EMI.